It is proposed to analyse the sources of Ca2 ion utilized in excitation-contraction coupling in smooth muscle, vascular and non- vascular, and to analyse possible changes in Ca2 ion utilization during the hypertensive state of spontaneously hypertensive rats. The comparative sensitivity of smooth muscle responses to K ion, NE and ACh as a function of (Ca2 ion) will be determined and compared to the relative sensitivities of these smooth muscles to the lanthanide cations. An attempt will be made to quantitate, using the "lanthanum" method the extent of Ca2 ion EXT utilized by a series of acetylcholine analogs in g.-p. ileal muscle. Changes in total and exchangeable Ca2 ion in vascular tissue from the spontaneously hypertensive rat will be determined with age and changes in vascular reactivity and an attempt made to determine whether the observed changes in vascular reactivity do correlate with any changes in Ca2 ion content or poor distribution.